Regards revising the error due to error

Hello Sir, this is a specific case. If a persons representative has filed ITR2 as NRE in this AY 2017-18 in july 2017, assessment is complete and refund granted. Now today after NRE returned to India, documents checked, it has been realized that there was an inadvertent mistake in calculating days of NRI as 181, there is actual shortfall of 20 days. Please advise what should be the best course of action now? The entire $ income becomes taxable I understand. (a) Can we revise/rectify the return after paying the tax. (b) We should just pay the tax with interest and leave it no ITR messing. (c) Meet the ITO and appraise him of the situation and the do as per what he says? (d) We should do nothing just sit quite.